The present invention is directed to the preparation of alpha,beta-dehydro-gamma-butyrolactone which, in turn, can be converted to gamma-butyrolactone by hydrogenation of the double bond. The alpha,beta-unsaturated lactone is useful as a solvent or monomer but, more particularly, upon hydrogenation the resulting gamma-butyrolactone is valuable to make the corresponding lactam as by reaction with ammonia. The lactam can be used to make fibers such as nylon fibers.
Previously gamma-butyrolactone has been made by converting gamma-hydroxycarboxylic acids to the lactone as follows: ##STR2## See, for example, Cason, Principles of Modern Organic Chemistry, Prentice-Hall, Inc., 1966.
Morrison and Boyd, Organic Chemistry, 2nd Ed., Allyn and Bacon, Inc., Boston, 1970, give the reaction as follows for the salt of a gamma-hydroxy acid: ##STR3##
Commercially gamma-butyrolactone is made from 1,4-butanediol by oxidative cyclization. However, the diol is believed to first be converted to the hydroxy acid before the cyclization occurs so that the cyclization would be as given in the above equations.
Previous methods of making alpha,beta-dehydro-gamma-butyrolactone, which may also be referred to as alpha,beta-butenolide, include a multistep process in which 3-butenoic acid is first converted into the corresponding epoxide by reaction with performic acid; the epoxide is then treated with hydrochloric acid to effect cyclization to a hydroxylactone, and finally this hydroxylactone is dehydrated over polyphosphoric acid to the unsaturated lactone. R. Palm, H. Ohse, and H. Cherdon Angew. Chem. Int. Ed. Engl. 5, (12), 994 (1966).